Dual-media network interfaces support two separate interfaces for a single port of a network device. For example, a single port of an Ethernet network interface may include a first interface for a copper medium and a second interface for a fiber optic medium. However, both interfaces may also support the same types of media. Dual-media network interfaces allow flexibility by providing a user with an option between two potentially different media. Additionally, dual-media network interfaces allow users to utilize redundant network connections. For example, if a first interface of a dual-media network interface fails, the dual-media network interface may be programmed to automatically switch to a second interface that includes a redundant network connection. Such redundant network connections reduce network downtime.
Some dual-media network interfaces include small form-factor pluggable (SFP) interfaces that support SFP modules. SFP modules are interchangeable plug-in transceivers that are typically hot-swappable and provide interfaces for desired media. For example, SFP modules commonly provide interfaces for high-speed fiber optic media. However, SFP modules provide interfaces for other media such as copper media. SFP modules allow a user to quickly and inexpensively repair or upgrade a network device. For example, if an SFP module fails, the SFP module can be replaced without soldering components. Simultaneous active links for a single port of a dual-media network interface can cause significant network disruption and/or downtime including a total network failure. Therefore, only one interface of a dual-media network interface is active at a time.
Referring now to FIG. 1, a dual-media network interface 10 includes a medium access control (MAC) device 12 that communicates with a physical layer device 14 (or PHY). The physical layer device 14 communicates with first and second interfaces 16 and 18. The first interface 16 (labeled “A” in FIG. 1) is an SFP interface between the physical layer device 14 and an SFP module 20. The second interface 18 (labeled “B” in FIG. 1) is illustrated as a medium dependent interface (MDI) such as a copper media interface, although the second interface 18 may be another type of interface. For example, the second interface 18 may be hardwired and controlled by the physical layer device 14. Conversely, the SFP module 20 includes an independent physical layer device 22 that controls network communications between the SFP module 20 and external devices.
As discussed above, it is undesirable for the first and second interfaces 16 and 18, respectively, to simultaneously establish links between the physical layer device 14 and external devices. In one approach, the physical layer device 14 utilizes link monitoring software to determine when either the first or second interface 16 or 18, respectively, establishes a link. For example, a processor 23 may execute the link monitoring software and communicate with the physical layer device 14 via management data input/output and management data clock (MDC/MDIO) signals.
The processor 23 is capable of reading registers in the physical layer device 14 via the MDC/MDIO signals in order to monitor links between the physical layer device 14 and external devices. For example, the link monitoring software may periodically poll the first and second interfaces 16 and 18 to detect when one of the first or second interfaces 16 or 18, respectively, establishes a link. When a link is detected at one of the first or second interfaces 16 or 18, respectively, the link monitoring software ceases communications via the other of the first or second interfaces 18 or 16, respectively. For example, the link monitoring software may cease communications via an interface 16 or 18 by disabling an internal module that is dedicated to the particular interface 16 or 18.
Since the second interface 18 is controlled by the physical layer device 14, the link monitoring software is capable of quickly and completely ceasing communications via the second interface 18 when a link is detected at the first interface 16. However, it is possible for the independent physical layer device 22 to retain a link with an external device even after the link monitoring software ceases communications via the first interface 16. For example, in order to disable the SFP module 20, the processor 23 may first transmit a signal to the MAC device 12, which is then forwarded to a disable pin 24 of the SFP module 20 (identified as TX_DIS in FIG. 1). In this case, an appreciable delay occurs from the time when the processor 23 first detects a link at the second interface 18 to the time when the MAC device 12 disables the SFP module 20 via the disable pin 24.
Additionally, the delay may be further extended when the processor 23 is busy processing other data unrelated to the dual-media network interface 10. For example, a network device 25 that includes the dual-media network interface 10 may include a large number of ports. In this case, the external device may still detect a link with the dual-media network interface 10 and attempt to send packets, which may create a disruptive renegotiation loop or other network congestion when the external device does not detect a response. Also, during the period of time both the first and second interfaces 16 and 18, respectively, are capable of establishing links on the same port, which can cause significant network disruption.